The present invention relates to image forming devices capable of multicolor image forming. More specifically, the present invention relates to thermal transfer type image forming devices employing a multicolor transfer material coated with coloring agents of different colors which thermally transfer the coloring agents on the transfer material to an object in succession, thereby forming a multicolor image on the object.
Conventionally, thermal transfer type image forming devices are small sized, low-priced, noisefree, and capable of image formation on ordinary paper. Therefore, this type of image forming devices has recently started to be practically used for electronic copiers, as well as for recording the output of computers, word processors, etc.
Some of these devices can form multicolor images by the use of a multicolor transfer material coated with coloring agents of different colors defining divisions of the same fixed area. One such conventional image forming device of this type uses a transfer material which is coated with yellow (Ye), magenta (Ma), cyan (Cy) and black (Bl) coloring agents successively arranged at regular intervals l, as shown in FIG. 1. In this transfer material, there are blanks or uncoated regions between the coloring agents and along both side edges of the material. In FIG. 1, the width of the border blanks is indicated by W1 (W1=0 is possible), while those of the marginal blanks are indicated by W2 and W3 (W2=W3 or W2=W3=0 is possible). Thus, color agent regions a (Ye), b (Ma), c (Cy) and d (Bl) with length x and width y are formed on the transfer material with those blanks between and around them. The transfer material also has nontransferable margins of widths W4, W5, W6 and W7 which are left around the coloring agent regions a, b, c and d, defining transfer regions a', b', c' and d' (hatched portions in FIG. 1) of length X0 and width Y0 which are actually used in the conventional image forming operation. In the transfer process, the object is centered in each of the actual transfer regions.
In one case, it may be required to form an image on an object of e.g. size A5 (half as wide as size A4) by using a transfer material of e.g. size A4. In another case, an instruction may be given to form an image which corresponds to a transfer region even smaller than size A5 by the use of the transfer material of size A4. In these cases, only the central portion (cross-hatched portion in FIG. 1) of each transfer region is used for the transfer, and those regions left untransferred cannot be reused. Thus, the prior art image forming apparatus is not very economical.